Gravitational Potential Energy
A construction crane lifts a steel beam of mass 500 kg vertically upward at constant velocity to a height of 30 m above the ground. Taking g as 10 m/s squared, what is the gain in gravitational potential energy of the beam?
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Solution
150000 J
As described in NCERT Class 11, Chapter 6 (Work, Energy and Power), the gravitational potential energy gained when an object is raised through a height h near Earth's surface is \cup = mgh. Substituting the values, \cup = 500 × 10 × 30 = 150000 J. Because the beam rises at constant velocity, its kinetic energy does not change, so all the work done by the crane against gravity is stored as potential energy. The option 15000 J results from omitting one zero in the height or mass. The option 1500 J drops two factors and is far too small. The option 75000 J wrongly uses half the height, perhaps by confusing this with a kinematic average. A magnitude check confirms the answer: lifting half a tonne by thirty metres should store a large amount of energy, and 1.5 × 10⁵ J is reasonable for an industrial crane lift.
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About This Question
- Subject
- physics
- Chapter
- work, energy and power
- Topic
- gravitational potential energy
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
150000 J
As described in NCERT Class 11, Chapter 6 (Work, Energy and Power), the gravitational potential energy gained when an object is raised through a height h near Earth's surface is \cup = mgh. Substituting the values, \cup = 500 × 10 × 30 = 150000 J. Because the beam rises at constant velocity, its kinetic energy does not change, so all the work done by the crane against gravity is stored as potential energy. The option 15000 J results from omitting one zero in the height or mass. The option 1500 J drops two factors and is far too small. The option 75000 J wrongly uses half the height, perhaps by confusing this with a kinematic average. A magnitude check confirms the answer: lifting half a tonne by thirty metres should store a large amount of energy, and 1.5 × 10⁵ J is reasonable for an industrial crane lift.
This easy difficulty physics question is from the chapter work, energy and power, covering the topic of gravitational potential energy. It appeared in the 2025 exam.
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